Conventionally, the sliding bearing used in turbochargers of internal combustion engines has been required to have corrosion resistance and wear resistance properties, and it has been made of brass in which grains of Mn—Si compounds are dispersed in a matrix of the brass. There has been proposed such a sliding bearing in JP-A-2003-42145, according to which an extension direction of crystallized Mn—Si compounds crystallized in brass is arranged to correspond to an axial direction of a rotating shaft to be supported by the sliding bearing on a sliding surface of the sliding bearing. The technique disclosed in JP-A-2003-42145 is schematically illustrated in FIG. 3 (in which SD denotes a sliding direction and AD an axial direction, crystallized Mn—Si compounds 2a are dispersed in a copper alloy matrix 1a). Depending on the direction of the crystallized Mn—Si compounds, an effect can be obtained, which effect is improvement of the wear resistance property of the sliding bearing.
With regard to the technique disclosed in JP-A-2003-42145, however, it was confirmed that in respect of the crystallized Mn—Si compounds, which exist on the sliding surface of the sliding bearing, and which extend to the axial direction of the rotating shaft, the larger the grain size (i.e. an extension length) increases, the more the wear resistance property is improved while the anti-seizure property is deteriorated.
During operation of the turbocharger of the internal combustion engine, the bearing use environment becomes a high temperature and the viscosity of lubricant oil drops. In the case where the oil viscosity excessively drops, an enough oil film is not formed in a clearance between the sliding surface of the sliding bearing and a mating shaft resulting in that both the sliding surfaces of the sliding bearing and the mating shaft are caused to directly contact. The sliding bearing disclosed in JP-A-2003-42145 has a disadvantage in that a sulfide film is hard to be formed on a surface of a brass matrix in the sliding surface of the sliding bearing, thus causing a contact of metals between the brass matrix and the mating shaft and thereby decreasing the anti-seizure property.